(1) Field of the Invention
This invention relates to an anthraquinonic colorant and a polarizing film containing the colorant in oriented condition.
(2) Description of the Prior Art
As the polarizing film which is commonly used today, polyvinyl alcohol is employed as the film base resin. Polarizing properties of the film are provided by the dichroic substances such as iodine compounds and/or the acid dyes or the direct dye which have selected structures.
Although these polarizing films exhibit excellent polarizing properties, they are insufficient in their durability. Therefore, in common, their durability is improved by covering both sides of the film with moisture-resistant film-like materials (protective membranes) which are transparent at least on one side. In other words, the internal polarizing film is very poor in durability and is guarded by the protective membranes or layers for practical durability.
Coupled with the recent widespread use of liquid crystal display elements for vehicles, computers and industrial instruments, improved durability of the polarizing film to prepare these elements is strongly desired, particularly, in terms of resistance against moisture, weather and heat. Polarizing films using a hydrophobic polymer as the film base resin have been proposed consequently, to improve these properties. Examples of these known arts include Japanese Patent Laid-Open No. 84409/1982 and the present inventors' applications such as Japanese Patent Laid-Open Nos. 68008/1983 and 125804/1985. While polarizing films according to these known applications have sufficient durability, they are not always satisfactory in view of their polarizing ability.